Calculating the MIPS Rating

I need some help with this problem I am trying to solve if anyone can help.

Each instruction on a certain computer system requires 1 cycle for any type of instruction. This system includes N processors and is used to execute a program contain 16 million instructions and 60% of the code can be executed in parallel. All of the processors run at a 4GHz clock rate. If the program is executed using only one of the processors, the execution time is observed to be twice that required when using all N processors to execute the program.
--What is the value of N?
--What would be the effective MIPS rating for this program on the single-processor system and on the N-processor system?

I'm not exactly sure what he's suggesting. The 2nd part of the question asks for mips rating for the single and N processor systems, so that's what I was trying to solve for. Can you offer me any guidance? Am I on the right track?